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Full text of "The Cambridge Natural History"

MOUTH AND TONGUE

61

be found at least traces of more cusps. Now in some of them
we may be dealing with instances of a complete tooth change;
the suppression, save for one tooth, which is found in Marsupials,
was probably not developed in at least some of these early
mammals. The simplicity may therefore have been preceded
by complexity, and may have been merely an adaptation to an
insectivorous diet.

Alimentary Canal.—The mouth of the Mammalia is remark-
able for the fact that with a few exceptions, such as the Whales,
there are thick and fleshy lips. The
office of these is to seize the food.
The roof of the mouth is formed by
the " hard palate" in front, which
covers over the maxillary and pala-
tine regions. This region is often
covered with raised ridges, which
have a symmetrical disposition, and
are particularly strong in Ruminant
animals. They are much reduced in
the Hodents, where the anterior part
of the palate is ill-defined owing to
the way in which its sides fade into
the lateral surface of the face. It
has been shown that these ridges,
in the Oat at least, develop as                         ,        ^

.,,.,»               ,            ..   f        ,   FIG. 40.—Palatal folds of tteBaccoon

separate papilliform outgrowths, and (Procyoniotor). p.p. Papilla paia-
it has been suggested that these **«; '•&. P?la*al folds- _(F^m

.,                    .

Wiedersheim's Structure of Man.)

has  been   suggested
papillae, which later become united
to form the ridges, are the last  remnant of palatine teeth such
as occur in lower vertebrates.
The tongue is a well-developed organ, usually playing a
double part. It acts as an organ of prehension, especially in
such animals as the Giraffe and the Anteater, where it is
long and protrusible beyond the mouth for a considerable dis-
tance. It also carries gustatory organs, which serve for the
discrimination of the nature of the food. Beneath the tongue
there may be a hardish plate, known as the sublingua. This is
especially prominent in the Lemurs, where it projects as a horny
structure below the tongue, and has an independent and Iree tip.
It is supported in some of these animals by a cartilaginous